Why are my Portfolio Sample Previews showing up blank? (On the screen before I send the delivery.)

[myusernamearts]

This is what happens when I upload a video file. It plays fine on my pc, but there’s nothing that’s actually playing in that little preview window when I press the play button.
(It’s suppose to be an animation without any sound.)

Say a buyer ends up accepting it for Live Preview, is it going to show up like a blank white screen?
Or is it just not gonna allow anything to show up?

Is there a way to format it differently to maybe get different results? (I use Movie Studio Platinum 12.0 and I went with the ‘XDCAM EX (.MP4)’ option because it was the only .mp4 that it said would fit a lot of my projects.)